Process of making artificial cryolite



Patented Nov. 20, 1923,

UNITED STATES PATENT; OFFICE.

HENRY HOWARD, OF CLEVELAND, OHIO, ASSIGNOR TO THE GRASSELLI CHEMICAL COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO.

PROCESS OF MAKING ARTIFICIAL CRYOLITE. v

No Drawing,

To all whom it may concern:

Be it known that I, HENRY In. he manufacture of artificial cryolite it is desirable to employ, as the source of the sodium component of the artificial cryolite,

a cheap sodium compound such as, the sodium salts of the strong mineral acids, and as the source of the fluorine component of the artificial cryolite, hydrofluoric acid gas or an aqueous solution of the same.

One method heretofore employed for the manufacture of artificial cryolite consists in combining sodium chloride, fluoride and hydrofluoric acid according to the equation This method, while making use of a cheap sodium salt and hydrofluoricacid gas or an aqueous solution thereof, does not produce true artificial cryolite but produces a product which contains a considerably reater proportion of aluminum than is inicated by the formula Al F .6NaF.

I have found that if artificial cryolite is formed in a reaction mixture which is substantially neutral or at least free from the bulk of the mineral acid generated by the action of hydrofluoric acid upon the sodium salt employed, i. e. sodium chlorid in the above mentioned reaction, artificial cryolite, the composition of which corresponds substantially to the formula Al F fiNaF, is formed.

My invention therefore comprises-formin artificial cryolite, using as the source of sodium a cheap sodium salt of a strong mineral acid, by the combination of suit- HoWAnD, a citizen of the United States, residing at' aluminum Application filed octob'er 16, 1922. Serial 1%. 594,982.

able reagents in a medium which is main? taircied substantially free of strong mineral acl The process, in general, comprises comblning aluminum fiuorid or reagents capable of forming aluminum fiuorid, such as aluminum hydrate and hydrofluoric acid, with the sodium salt and hydrofluoric acid in quantit suflicient to convert the sodium of the so ium salt to sodium fiuorid and a neutralizing agent in quantit sufiicient to neutralize the acid. generated hydrofluoric acid upon the sodium salt.

A process in which the inexpensive, sodium salts, such as sodium chlorid, sodium nitrate, or sodium sulfate or mixtures thereof are employed to supply the sodium component of the artificial cryolite, is preferred.

Several processes may be employed for carrying out the invention some of which are illustrated in the, following examples.

Ewawle 1. p

I first prepare separate neutral solutions of aluminum fiuorid and ammonium fiuorid by dissolving aluminum hydrate and ammoniain separate batches of hydrofluoric acid solution. Or, if desired, a neutral solution containing both aluminum fiuorid and ammonium fiuorid may be prepared by dissolving one molecular equivalent of aluminum hydrate (Al O .3H O) and six molecular equivalents of ammonia (NH in twelve molecular equivalents of hydrofluoric acid (HF). The separate neutral solutions of aluminum fiuorid and ammonium fiuorid or the neutral solution con taining both salts are then mixed with a neutral solution of a sodium salt, for example, sodium chlorid; in the proportions represented by the equation whereby an artificial cryolite precipitate and a solution of ammonium chlorid are formed. The artificial cryolite is separated from the solution in any suitable manner and is washed and dried. The mother liquor and wash water arev treated for the recovery of ammonium chlorid which forms a valuable by-product of the process.

Instead of preparing neutral solutions of aluminum fiuorid, ammonium fiuorid and by the action of the -dissolvi one molecular the sodium salt as described above, the for- Emample 2. v

I. dissolve six molecular equivalents of a sodium salt such as sodium chlorid in six molecular equivalents of hydrofluoric acid solution an neutralize the hydrochloric acid generated with six molecular equivalents of ammonia and mix the resulting solution with a solution containing one molecular equivalent of aluminum fluorid respectively six molecular equivalents of ammonia and s1x molecular equivalents of a sodium salt, such as sodium chlorid, or a single solution containing six. molecular equivalents of sodium chlorid and six molecular equivalents of ammonia. A satisfactory rocedure for carrying vout the process is as iollows: 1

In one vessel I prepare a solution of aluminum fluorid in hydrofluoric acidby equivalent of Al O .8 in twelve molecular equivalents of HF. In a separate vessel I prepare a solution of sodium chlorid in water con taining six molecular equivalents of NaCl. The aluminum fluoridsolution containing an excess of hydrofluoric acid suflicicnt to convert the sodium chlorid to sodium finorid is then slowly added to the sodium chlorid solutionwith constant stirring simultaneously with the addition of ammonia to the mixture, the rate of addition of ammonia being regulated to maintain the reaction mixture slightly acid to avoid loss of ammonia until all of the aluminum fluorid solution has been added, whereupon enough ammonia is added to neutralize the reaction mixture. After the reaction is complete and the reaction mixture has been neutralized, the artificial cryolite is separated, washed and dried and the mother liquors and wash waters are treated for the recoveryof ammonium chlorid. The composition of the artificial cryolite product corresponds substantially with the formula A1 F .6NaF.

It will be apparent'that if sodium salts otherthan sodium chlorid are used in .the process the corresponding ammonium salts will result as by-products. For instance, if sodium nitrate is used the by-product will be ammonium nitrate. It is of course withi in the scope ofmy invention to employ impure sodium salts or mixtures of sodium salts.

It will be noted that in each of the several procedures outlined in the above examples the combination of sodium fluorid with aluminum fluorid to form artificial cryolite takes place in a substantially neutral solution and also that in each instance an inex pensive sodium salt of a strong mineral acid is employed as the source of the sodium component of the artificial cryolite. The process requires a neutralizing agent which should be incxpensive or which forms, by combination with the acid component of the sodium salt used, a valuable by-product, preferably both., A suitable neutralizing agent which answers theserequirements is ammonia, preferably in the form of crude ammonia liquors.

The advantages of my process are (1) the production of substantially true artificial cryolite; (2) simple and inexpensive operation; (3) the use of inexpensive raw materials, to wit, crude hydrofluoric acid, crude ammonical liquors and inexpensive sodium salts; and (4) the production of valuable ammonium salts as by-products. 1

This application is a continuation in part of my application Serial No. 538,646, filed February 28, 1922.

I claim: 1. Process of making artificial cryolite which comprises mixing solutions of aluminum fiuorid, ammonium fiuorid and a sodium salt of a strongmineral acid, and separating artificial cryolite from the mixture. 2. Process as defined in claim 1 in which the sodium salt is sodium nitrate.

mineral acid containing six atomic equii alents of sodium, and recovering artificlal cryolite and the ammonium salt of said stronfi mineral acid from the mixture' 5 5.

rocess as defined in claim 4 in which the sodium salt is sodium nitrate.

6. Process oi it a artificial cryolite which comprises comhinin aluminum fluorid, ammonium fiuorid, an a, sodiu salt of a strong mineral acid in a solution substantially free of acid.

In testimony whereof, I a my signature.

MNRY HOWARD. 

